Nanosilver

Nanosilver is a nanoparticle of silver that is used for its antimicrobial properties in hospitals and consumer products (including odor-resistant clothing, hand sanitizers, water treatment systems, and even microbe-proof teddy bears). Nanoparticles are between one and 100 nanometers, i.e. between one and 100 billionths of a meter. Around the world, nanosilver is a growing environmental and health concern. In the U.S., manufacturers do not have to disclose the use of nanoparticles on product labels. Recent findings show that silver nanoparticles may negatively impact plant growth when they enter the environment. [1] In lab studies, silver nanoparticles are highly toxic to bacteria and fungi, both of which are critical to plant growth, particularly in organic agriculture. Nanoparticles such as nanosilver often enter the environment via wastewater and sewage sludge.[2]

Nanosilver Treatment of Textiles

In 2010, the company HeiQ Materials AG submitted an application to register a nanosilver treatment of fibers as a pesticide in the United States. The EPA approved a conditional registration of the nanosilver treatment, HeiQ AGS-20 in 2012.

Nanosilver in Washing Machines

Samsung markets its "SilverCare" washing machines as able to remove 99.9 percent of bacteria.[6] The washing machines release 400 billion nano-sized silver ions in each load of laundry. However, when another company, Fisher and Paykel, looked into the usefulness of nanosilver in washing machines compared to regular washing machine technology, they found that washing clothes at 20C (68F) with detergent removed 99.79 percent of bacteria.[7] Thus, they determined, using nanosilver was not worth the environmental cost.

Antibacterial Wound Dressing Gel

Environmental Effects

Despite its widespread use, relatively little is known about the environmental effects of nanosilver.[9] The U.S. EPA sets water quality criteria at 1.9 parts per billion of silver in salt water and 3.4 parts per billion in fresh water. However, these standards are for silver in general, not nanosilver in particular. As nanosilver is toxic to microbial life, it could have a significant impact on the environment. Some top experts do not think the EPA standards on silver are protective enough to spare the environment from harm.[10]

Toxicity to Fish

A study at Purdue University found that nanosilver particles suspended in solution were toxic, even lethal, to fathead minnows (a species of fish).[11] Once the nanosilver settled, it became much less toxic, but still toxic, to the minnows. Researchers tested the minnows at various life stages. They found that the nanosilver particles were so small they were able to cross the egg membranes and move into the fish embryos in less than a day.

Effect on Plants and Soil Life

Another study measured the effects of plants grown in either sludge or sludge plus nanosilver.[12] The tub of plants with nanosilver showed less microbial activity (compared to the other tub) but also off-gased four times as much nitrous oxide, a potent greenhouse gas that is 296 times stronger than carbon dioxide.[13]

Nanosilver in Effluent and Sewage Sludge

In one study, six types of commercially available socks contained up to a maxiumum of 1360 parts per million of nanosilver and leached as much as 650 µg of silver into 500 mL of distilled water.[14] Both colloidal and ionic silver leached from the socks, with particles ranging from 10 to 500 nanometers in diameter. The study was designed to simulate the amount of nanosilver entering wastewater treatment plants. Wastewater treatment plants likely release nanosilver into the environment either in the form of effluent or sewage sludge.

In comments to the EPA, officials from the sewage industry expressed concern about the increased use of silver, particularly nanosilver, as a pesticide in household products.[15] The comments note that when the wastewater treatment plant is successful at removing silver from wastewater, all that does is remove the silver from the effluent only to put it into sewage sludge. The sewage industry worries that high concentrations of silver in sewage sludge will make them unable to dispose of sludge via land application. The letter says: "Widespread use of household products that release silver ions into sanitary sewer systems could increase silver concentrations in POTW influents, effluents, and biosolids. If silver pesticide product use becomes common, wastewater silver discharges could reach levels not seen in the last two decades—and could have adverse impacts on our wastewater treatment process as well as on the quality of our effluent and biosolids." The letter goes on to note that most silver used in products will ultimately make its way to wastewater treatment facilities, as it does not biodegrade.

They add that "two related studies, Choi and Hu (2008)[16] and Choi et al. (2008)[17] found that silver particles less than 5 nanometers in diameter are uniquely toxic to nitrifying bacteria, which are critical to biological nutrient removal at POTWs [publicly owned wastewater treatment plants]." Furthermore, they note that particle size impacts silver's toxicity to aquatic organisms and that wastewater treatment plants may not be able to remove silver from wastewater if the particles are very small.

Human Exposure and Toxicity

One study found that fabrics containing nanosilver can release nanosilver when exposed to artificial human sweat.[18] However, it is not known if nanosilver can be absorbed through skin. Another study published in 2010 found that nanosilver is toxic to human stem cells and toxicity increases the longer the nanoparticles are stored.[19] A 2009 study compared silver with the known neurotoxicant pesticide chlorpyrifos, finding that silver is five times more toxic than chlorpyrifos.[20] According to the study's findings, silver has the potential to kill developing nerve cells. While it would require a lot of silver to harm an adult, silver can pass from a mother to a developing fetus, and the fetus would require far less silver than an adult to suffer harm. Some evidence shows that nanosilver interferes with DNA replication.[21]

Government Regulation

The nanosilver in clothing already on the market in the United States is not yet regulated. NPR reported that the EPA motioned that it would begin the process of writing rules soon, although it had not done so at that time.[22]

In 2008, the [International Center for Technology Assessment] (ICTA) petitioned the EPA to classify nanosilver as a pesticide and regulate it as such.[23] In August 2010, the U.S. EPA announced it was considering granting "conditional approval" to the Swiss company HeiQ Materials AG, a producer of nanoparticles, for the use of nanosilver as a pesticide in fabrics.[24] The EPA has the authority to regulate nanomaterials under the Toxic Substances Control Act (ToSCA) and the Federal Insecticide Fungicide and Rodenticide Act (FIFRA).[25] The EPA granted a conditional registration of HeiQ's nanosilver in 2011.[26] In 2012, BNA.com reported that the White House was blocking EPA efforts to regulate nanosilver.[27]

Marketing and Influence by Industry

Industry trade groups, such as the Silver Nanotechnology Working Group say that "nanosilver used as a microbicide shouldn’t be regulated more strictly than colloidal silver, particles of silver in solution a well established ingredient present in including in health supplements and other products."[28]

Nanosilver as "Green"

In some instances, industry now markets nanosilver as a "green," ecofriendly, or even organic technology.[29] The logic used behind such an idea implies that nanosilver is harmless both to humans and the environment, and it is used in place of chemicals like chlorine bleach, triclosan, or detergent that would be "worse" for the environment. While each of these chemicals has an environmental impact, it is important to note that nanosilver does not break down in the environment whereas other chemicals may.